Several methods are known for carrying out observation of gelation process or gel state based on the two dimensional light scattering intensity. For example, there are a method for observing gelation process and state of a non-ergodicity sample (JP-A-2000-214086), a method for measuring gelation degree of polyvinyl chloride (JP-A-10-120795) and the like, but these are methods for measuring luminance distribution at a predetermined scattering angle making use of the angle-dependency of transmitted scattered light of a thin film sample. Some cases of the use of light scattering have been disclosed on the analyses of agarose gel formation process (cf. homepage of Otsuka Denshi, retrieved on Mar. 16, 2002, http://www.photal.co.jp/product/calls-6-1.html) and curd formation process of milk (Journal of Food Science and Technology (written in Japanese), vol. 39. no. 4, pp. 309-315). However, these are also on the evaluation of scattering light intensity based on the angle-dependency of transmitted scattered light.
In the conventional techniques, light can hardly penetrate into, for example, a high turbidity material body or a hardly light-permeable or thick massive gel material body or gel-forming sol material body, so that it was difficult to evaluate its angle-dependency of transmitted scattered light. In addition, there were problems in that the samples are limited to thin sections, the device becomes complex for the evaluation of angle-dependency, it is difficult to carry out the measurement on the production line due to a prolonged period of time for the measurement, useful information is deleted depending on the limitation of angle, and the like.
Speckle pattern is a phenomenon in which, when a coherent light forms an image on a rough surface, it complicatedly scatters and interferes with one another depending on the roughness, so that spots having strong brightness (speckles) are generated in a large number as a spatial distribution of irregularly reflecting light, thus forming a spot pattern having contrast (so-called speckle pattern). For example, speckles are removed as a noise in a method in which the structure of a starch dispersion or collagen gel is analyzed by light scattering measurement (JP-A-7-301602). Thus, speckle has been treated as a noise of light and the like electromagnetic wave and supersonic wave, but measurements of displacement, distortion and roughness have recently been introduced as its applied measuring techniques (illustrative examples are not described; “Practical Light Keyword Dictionary” (written in Japanese), published by Asakura Shoten, pp. 202-203). Also, its application to non-contact type migration length (speed) measurement, vibration measurement and the like based on speckle patterns has been devised in a large number. In addition, application of a specific speckle pattern to the recognition of a material or a person has also been devised (JP-A-2000-149087).
On the other hand, the present inventors have recently disclosed a method for discriminating quality of gel shape food or sol shape food (Japanese Patent Application No. 2001-301653), which is a spectral absorption method for evaluating qualities from the absorbance at a specified wavelength of transmitted reflected light.
In this connection, virtually nothing is known about a case in which shapes of formed image or speckle patterns of irradiated light generated by complex scattering and interference of light are employed and applied to the analysis of conditions of gel material bodies and changes thereof, like the invention, and completely no information is available concerning a case in which they were applied to gel shape food or sol shape food (e.g., bean curd (tofu), soybean milk or the like).
Regarding quality of a gel shape material body such as a gel shape food product, its mouth-feel is evaluated generally by synthesizing its physical properties, appearances (shape and color), odor and taste. Particularly, influences of hardness, elasticity and the like physical properties upon the mouth-feel and quality value are great. For example, packed tofu (bean curd) is produced by mixing cooled tofu with a coagulant, filling and packing the mixture and then effecting coagulation of the contents by heating, and too soft, un-coagulated, unevenly coagulated and the like rejected articles are generated on rare occasions due to a change in the soybean quality or an artificial mistake. In addition to this, the same problems are occurring on a large number of polymer gel material bodies.
Regarding material bodies which generate a sol-gel conditional change, a step for changing from sol to gel is contained in the production process of the majority of gel products, and management of the step has been carried out relying on experience and perception of each worker. In case that this step can be objectively measured, it will become useful information on the quality control. In addition, there is a case in which a sol or liquid food article (a drink) becomes a rejected article due to its gelation (coagulation) by an unexpected cause during its processing process or preservation of its package. On the contrary, there is a case in which a material body which formed a gel state become a rejected article due to its conversion into a sol state caused by stirring, external force, heating and the like.
In the case of processed products, exclusive inspectors are carrying out exclusion of rejected articles by sampling inspection (opening the package) or by a feel or with the naked eye without opening. However, in addition to the personnel expenses, in case that a rejected article is shipped to the market by some chance, it will become a claiming problem and cause a danger of incurring serious damages such as reduction of business image and trust, a demand for a large security money, a suspension of business and the like.
In the case of food, hardness, taste and the like qualities are checked by carrying out a destructive test and a sampling test through a sampling inspection as a preventive measure even in the usual quality control, but this cannot be said sufficient because of the problems in that it requires time until the results are obtained, an inspection omission cannot be wiped out and all products of the rejected lot have to be discarded.
However, there is no inexpensive measuring method known in the prior art, for the non-destructive, non-contact, automatic and quick judgment of the qualities of gel state material bodies and material bodies capable of causing changes in the sol-gel state, such as gel-shape food and sol shape food.
In this connection, the speckle pattern is defined as “A complex interference pattern which is formed as a pattern of spots having high contrast in the space when a rough surface is illuminated with a laser beam or the like coherent light, due to interference of lights scattered at respective points on the rough surface with a mutual irregular phase relationship.” (“Dictionary of Light” published by Ohm (written in Japanese), pp. 126-127), and “When laser beam is applied to the rough grind surface of paper, frosted glass, a wall, wood, a metal or a plastic material, a pattern of spots which cannot usually be observed shows up. Each spot is generally called as a speckle, and the pattern as a speckle pattern. This pattern is formed, because the lights scattered at respective points on the scattering surface interfere with one another having a irregular phase relationship corresponding to the microscopic irregularity on the surface.” (“Optical Measurement Handbook” published by Asakura Shoten (written in Japanese), p. 234).
However, it is described that “Fineness of the pattern is not related to the surface roughness and the like microscopic structures of the surface but determined by the shape and size of irradiated spots on the surface, and the pattern becomes rough as the spots are reduced.” and “When pint of the image formation system is turned away from the diffusing surface, the image becomes blurred, but the speckle is clear as usual.” (“Optical Measurement Handbook” published by Asakura Shoten (written in Japanese), p. 234).